the year 2000, the now-developing areas may well number some 5.4 billion persons; the economically advanced nations, some 1.6 billion. Thus, while the modernized nations will increase by some 600 million during the next 30 years, the developing nations could increase by about 3 billion or five times as much.
The accelerating growth in human numbers is shown by comparing observed and projected annual increases. Between 1900 and 1950 the population of the world grew by some 20 million persons per year. On the basis of the projections we have cited, it could increase by an average of 90 million per year during the second half of this century, and by as much as 150 million per year during the first 20 years of the 21st century.
Birth Rates and Death Rates
World population growth is entirely the result of natural increase—the excess of births over deaths. For any subdivision of the world, net migration—the difference between out- and in-migration—is also a factor.
The population "explosion" is, in general, the result of great declines in death rates along with continuing high birth rates. When death rates began to fall, as they did in European populations in the 18th and 19th centuries, and in non-European populations in the 20th, more and more children survived to adulthood and were themselves able to produce children.
Among Europeans and populations of European stock, death rates declined rather slowly, requiring many decades to fall from 30-35 per 1,000 to the 15-20 per 1,000 typical of most less developed countries today.
Populations of European stock and, more recently, Japan have largely completed what demographers call the "demographic transition." Birth rates have declined from highs of 30 to 40 or more births per 1,000 population to below 20 per 1,000. Since death rates in these populations have now declined to the level of 10 per 1,000, annual growth rates are 1 percent or less, compared with 2 to 3.5 percent in less developed countries.
The great reductions in mortality did not reach the two thirds of mankind in the developing nations in Asia, Latin America, and Africa until after World War II. In general, birth rates have remained high, with the result that these areas are experiencing higher rates of natural increase than ever characterized the developed countries of today. Latin America, the most rapidly growing continental region, at 3 percent per year, will double its population in about 23 years.
The Recent Decline in Mortality in Less Developed Countries
The average expected lifetime at birth (life expectancy) for the population of India in 1910 was about 22 years, probably not much different from what